This invention relates to a jet propulsion system for a watercraft and more particularly to an improved device for minimizing the sounds and vibrations generated by the jet propulsion unit.
Jet propulsion units are quite popular in connection with the propulsion of watercraft and especially a particular type of watercraft referred to as a xe2x80x9cpersonal watercraftxe2x80x9d. These types of watercraft generally are designed to be operated by a rider who may carry no more than one to three additional passengers. Frequently these passengers are seated in straddle, tandem fashion on a longitudinally extending seat that is formed at the rear of the watercraft with the propulsion unit being disposed beneath the seat.
One problem particular with this type of construction can be best understood by reference to the aforenoted copending application. As noted therein in conventional constructions the water inlet passage through the lower part of the watercraft hull curve upwardly from their inlet opening and directly registered with the impeller housing of the jet pump in close proximity to its impeller. It has been found that this causes pulsations in the water that is transmitted back through the forward wall of the bulkhead that separates the jet pump from the engine compartment and can create unpleasant vibrations in the watercraft and sounds that are undesirable.
It is, therefore, a first principal feature of this invention to provide an improved and low cost jet propulsion unit for a personal watercraft that avoids these pulsations.
It is a further object of this invention to provide an arrangement for utilizing this feature in conjunction with conventional type jet pumps so as to not require a redesign in either the hull or the jet pump in order to use the feature of the invention.
The copending application presents a solution to this problem, but further improvements are desirable. It is therefore another object of this invention to provide such further improvements.
This invention is adapted to be embodied in a personal watercraft that is comprised of a hull having an undersurface including a vertically extending bulkhead defining in part a rear portion of an engine compartment containing a prime mover. The hull undersurface defines at least in part a downwardly facing water inlet opening through which water may be drawn and a curved discharged path that curves upwardly from said water inlet opening toward the bulkhead. A support plate is fixed to the rear side of the bulkhead. An extension housing is affixed to the support plate at one end thereof. A jet propulsion system is carried by the other end of the extension housing. The jet propulsion system is comprised of an outer housing having an impeller portion, an impeller rotatably journalled about an impeller axis in the impeller portion and driven by the prime mover and a discharge nozzle portion positioned rearwardly of the impeller though which the water pumped by the impeller is discharged for propelling the personal watercraft. The support plate and the extension housing defining a water opening path leading in a direction parallel to the impeller axis and having a shape that constitutes generally an extension of the opening of an inlet to the impeller housing portion so as to isolate the pulsations generated by the impeller. The water opening path has a length greater than the axial length of the impeller.